The Monarch Butterfly migration of Fire Island.
There’s no place like an island, and a barrier island especially, for seasonal migrants. That’s certainly true of Fire Island. The thirty-two-mile-long sandbar off Long Island may be best known for little red wagons, houses on stilts, and gay beach parties, but it is also beloved by lepidopterists. Every September and October, the island’s dunes become a way station for tens of thousands of monarch butterflies, who stop there on their three-thousand-mile journey from Canada to a mountaintop in Michoacán, near Mexico City, where they go to reproduce and die.
From mid-August through late September or early October, thousands of these delicate insects stop to rest and feed on Fire Island as they make their way south for the winter. For the butterflies you see on Fire Island, this is a journey of more than 2,500 miles! The beautiful orange and black adult monarchs we see fluttering above the dunes on Fire Island each fall are flying south to the safety of Oyamel Fir Forests, dense stands of evergreens found at high altitudes in the mountains of central Mexico. There, the butterflies cluster together in the trees for safety from predators and from the elements. The following spring, with warmer temperatures and increasing day length the overwintering butterflies adults emerge from the forests and begin their multi-generational return trip north.
The monarchs that overwintered in Mexico will breed and lay eggs along their journey north. It is their offspring and successive generations that continue the northerly journey to the northern United States and Canada. Unlike the fall monarch migrants that can survive for up to nine months, their northbound relatives live for two to five weeks before reproducing. Eggs are laid on milkweed plants and hatch to become larvae, or caterpillars, that feed solely on the leaves of milkweed to support their rapid growth. The caterpillar then attaches itself to a milkweed plant and transforms into a blue-green chrysalis. It takes about a month for monarchs to progress from the egg stage to adult butterfly.
- Monarchs, like all other butterflies and moths, go through egg, larval (caterpillar), chrysalis (cocoon), and adult stages.
- Monarch caterpillars ingest milkweed that contains a toxic compound. The presence of this toxin is used by the monarch butterfly as a defense against predators.
- Other butterflies, such as the Viceroy, mimic the Monarch’s colors to pretend that they are also toxic to predators.